Dynamic lens for head mounted display

ABSTRACT

A Head Mounted Display (“HMD”) includes a display module, an optical combiner, control circuitry, and a lens. The display module generates image light and the optical combiner is for combining the image light with external scene light. The lens is positioned to receive the image light. The lens is capable of dynamically changing at least one lens property of the lens. The control circuitry controls the lens to dynamically change at least one lens property of the lens.

TECHNICAL FIELD

This disclosure relates generally to optics, and in particular but notexclusively, relates to Head Mounted Displays.

BACKGROUND INFORMATION

A head mounted display (“HMD”) is a display device worn on or about thehead. HMDs usually incorporate some sort of near-to-eye optical systemto form a virtual image located somewhere in front of the viewer. Singleeye displays are referred to as monocular HMDs while dual eye displaysare referred to as binocular HMDs. Occlusion HMDs, also called immersionHMDs, project a virtual image over a black background (the projectionoptics are not see-through). See-through HMDs also project a virtualimage, but they are at the same time transparent (or semi-transparent)and the projection optics are called combiner optics, since they combinethe virtual image over the reality. Augmented reality is one aspect ofsee-through HMDs, where the virtual image is super-imposed to thereality.

HMDs have numerous practical and leisure applications. Historically, thefirst applications were found in aerospace applications, which permit apilot to see vital flight control information without taking their eyeoff the flight path (these are referred to as Helmet Mounted Displaysand are often used for rotary wing aircrafts). Heads Up Displays(“HUDs”) are usually used in non-rotary wing aircrafts such as planesand jet fighters, where the combiner is located on the windshield ratherthan on the helmet. HUDs are also used in automobiles, where the opticalcombiner can be integrated in the windshield or close to the windshield.Public safety applications include tactical displays of maps and thermalimaging. Other application fields include video games, transportation,and telecommunications. There is certain to be newfound practical andleisure applications as the technology evolves; however, many of theseapplications are limited due to the size, weight, field of view, andefficiency of conventional optical systems used to implement existingHMDs.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting and non-exhaustive embodiments of the invention aredescribed with reference to the following figures, wherein likereference numerals refer to like parts throughout the various viewsunless otherwise specified.

FIG. 1A depicts a top cross-section view of an example optical combinerincluding a display module, a light relay, a beam splitter, and an endreflector.

FIG. 1B illustrates a computer generated image directed into aneyeward-region of an estimated field of view of a user of an opticalcombiner.

FIG. 2A illustrates control circuitry controlling a tunable lens thatreceives image light to be directed into an eyeward-region, inaccordance with an embodiment of the disclosure.

FIGS. 2B-2E illustrate examples of tunable lenses that can be utilizedas the tunable lens in FIG. 2A, in accordance with an embodiment of thedisclosure.

FIG. 2F illustrates computer generated images directed into differentdepths of the same eyeward-region by a tunable lens, in accordance withan embodiment of the disclosure.

FIG. 3A illustrates control circuitry controlling a stacked switchablelens that receives image light to be directed into differenteyeward-regions, in accordance with an embodiment of the disclosure.

FIG. 3B illustrates a display module and control circuitry controllingan example stacked switchable lens that includes three switching optics,in accordance with an embodiment of the disclosure.

FIG. 3C illustrates an example switching optic configuration that can beutilized within a stacked switchable lens, in accordance with anembodiment of the disclosure.

FIG. 3D illustrates computer generated images directed into differenteyeward-regions that are stitched together, in accordance with anembodiment of the disclosure.

FIG. 3E illustrates computer generated images directed into differenteyeward-regions that are not stitched together, in accordance with anembodiment of the disclosure.

FIG. 4A illustrates a display module launching image light and controlcircuitry coupled to control a reconfigurable lens positioned to directthe image light into different eyeward-regions, in accordance with anembodiment of the disclosure.

FIGS. 4B-D illustrate example reconfigurable optic configurations thatcan be utilized in the reconfigurable lens in FIG. 4A, in accordancewith an embodiment of the disclosure.

FIG. 5 depicts a top view of a user wearing a binocular head mounteddisplay that includes a dynamic lens, in accordance with an embodimentof the disclosure.

DETAILED DESCRIPTION

Embodiments of a Head Mounted Displays that include dynamic lenses aredescribed herein. In the following description, numerous specificdetails are set forth to provide a thorough understanding of theembodiments. One skilled in the relevant art will recognize, however,that the techniques described herein can be practiced without one ormore of the specific details, or with other methods, components,materials, etc. In other instances, well-known structures, materials, oroperations are not shown or described in detail to avoid obscuringcertain aspects.

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure, orcharacteristic described in connection with the embodiment is includedin at least one embodiment of the present invention. Thus, theappearances of the phrases “in one embodiment” or “in an embodiment” invarious places throughout this specification are not necessarily allreferring to the same embodiment. Furthermore, the particular features,structures, or characteristics may be combined in any suitable manner inone or more embodiments.

FIG. 1A depicts a top cross-section view of an example optical combiner100 including a display module 105, a light relay 165, a beam splitter131, and an end reflector 183. Optical combiner 100 may be integrated ina head gear to form a head mounted display (“HMD”). Display module 105projects computer generated images (“CGI”). Display module 105 may beimplemented by a light emitting diode (“LED”) array, an organic LED(“OLED”) array, a quantum dot array, a laser scanner, or otherwise.Display module 105 may also be implemented by a light source (e.g.laser, LED, or bulb) backlighting an LCD display or a liquid crystal onsilicon (“LCOS”) panel reflecting a light source. Display module 105 maybe considered a “micro-display.” End reflector 183 may be a concavemirror.

In operation, display module 105 launches display light (which may beCGI light) along a forward path 180 toward end reflector 183. Lightrelay 165 may have a transparent structure to permit most or a largepart of the display light to pass through along forward path 180. Lightrelay 165 may be fabricated of a solid transparent material (e.g.,glass, quartz, acrylic, clear plastic, PMMA, ZEONEX-E48R, etc.) or beimplemented as a solid housing having an inner air gap through which thedisplay light passes. Light relay 165 may operate to protect the opticalpath, but may not necessarily use total internal reflection (“TIR”) toguide or confine the display light.

Along forward path 180, display light encounters beam splitter 131. Beamsplitter 131 reflects a first portion of the display light towards theexternal scene-side of optical combiner 100 and passes a second portionof the display light. Beam splitter 131 may be a 45 degree 50/50non-polarizing beam splitter, meaning it reflects 50 percent of lightand passes the other 50 percent of light. The display light passed bybeam splitter 131 continues along forward path 180 and end reflector 183reflects back the display light along a reverse path 185. The displaylight along reverse path 185 encounters beam splitter 131, whichreflects a portion of the display light along reverse path 185 toward aneye-ward side of optical combiner 100. The illustrated embodiment ofFIG. 1A allows the display light launched by display module 105 to beprojected into eye 160 of a user, which is how a computer generatedimage is directed into eyeward-region 176. In addition to directingimages into eyeward-region 176, optical combiner 100 may also allow atleast a portion of external scene light 155 to reach eye 160 (after aportion is reflected by beam splitter 131).

FIG. 1B illustrates a computer generated image directed intoeyeward-region 176 which is in an estimated field of view (“FOV”) 190 ofa user of optical combiner 100. In FIG. 1B, FOV 190 and eyeward-region176 are defined within an x-y plane. A typical user of an HMD may have anatural field of view (“FOV”) of nearly 180° horizontally. An imagepresented within eyeward-region 176 from optical combiner 100 may onlybe presented to the user in 15° (horizontally) of the user's total FOVand only within the x-y plane. In certain contexts, it would beadvantageous to present images and information to a user in differentdepths (z-axis) of FOV 190 and in more than 15° (horizontally) of theuser's total FOV.

FIG. 2A illustrates control circuitry 250 controlling a tunable lens 233that receives image light 207 to be directed into an eyeward region 276,in accordance with an embodiment of the disclosure. Display module 205generates image light 207 that propagates through tunable lens 233 andcombiner 230 includes a reflective element 235 that directs image light207 to eyeward region 276. Reflective element 235 is a flat 50/50 mirrorthat reflects fifty percent of incident light and passes the remainingfifty percent of incident light, in some embodiments. Combiner 230 maybe integrated as an eyepiece in a monocular or binocular HMD. Combiner230 may be generally transparent and fabricated of a solid transparentmaterial (e.g., glass, quartz, acrylic, clear plastic, PMMA,ZEONEX-E48R, etc.). The generally transparency of combiner 230 allowsexternal scene light 155 to propagate to eye 160 to allow a user to viewher environment when combiner 230 is in front of a user's eye 160. Ifreflective element 235 is also partially transparent (e.g. passing fiftypercent of incident light), it will also allow some of external scenelight 155 to propagate to eye 160. Display module 205 may be implementedby a light emitting diode (“LED”) array, an organic LED (“OLED”) array,a quantum dot array, a laser scanner, or otherwise. Display module 205may also be implemented by a light source (e.g. laser, LED, or bulb)backlighting an LCD display or a liquid crystal on silicon (“LCOS”)panel reflecting a light source. Display module 105 may be considered a“micro-display.”

Control circuitry 250 may include a processor, a Field Programmable GateArray (“FPGA”), or other processing logic. Control circuitry 250 mayinclude buffers and/or memory to store instructions, settings, images,and other data. In FIG. 2A, control circuitry 250 is coupled to atransmissive tunable lens 233 and configured to adjust a focal length oftunable lens 233 to focus image(s) included in image light 207 atvarying focus depths. Control circuitry 250 sends a focus signal 254 totunable lens 233 to adjust the focal length of tunable lens 233. Focussignal 254 may be digital or analog. The focal length of tunable lens233 may be continuously variable in response to focus signal 254. In oneembodiment, tunable lens 233 has defined discrete focal length positionsthat it can switch between in response to focus signal 254.

Tunable lenses can be purchased from VariOptic of France, for example. Astretchable radially symmetric membrane (not illustrated) developed byOptotune of Switzerland can also be utilized as tunable lens 233.

FIGS. 2B-2E illustrate examples of tunable lenses that can be utilizedas tunable lens 233, in accordance with an embodiment of the disclosure.FIG. 2B illustrates a liquid crystal (“LC”) tunable lens 248 thatincludes liquid crystals 249. Liquid crystals 249 are disposed in aregion 245 and a region 244 between two electrodes 247. The first of thetwo of the electrodes 247 is flat and on the receiving side of tunablelens 248, while the second electrode is curved. The exiting side oftunable lens 248 (where the S-polarized display light exits) is oppositeof the receiving side of tunable lens 248 and is parallel to thereceiving side. When tunable lens 248 is unswitched (no voltage isapplied across the electrodes 247), S-polarized light received by thelens encounters the same refractive index as the liquid crystals 249 inboth regions 244 and 245 are oriented similarly. Therefore, tunable lens248 is substantially transparent and offers substantially no opticalpower to the received S-polarized light because the receiving side andthe exiting side are parallel and the refractive index in regions 244and 245 between the receiving side and exiting side are the same.However, when tunable lens 248 is switched (a voltage is applied acrosselectrodes 247), the orientation of the liquid crystals 249 in region244 changes, which effects the refractive index encountered byS-polarized display light. Since region 244 is shaped like a lens andhas a different refractive index than region 245 while a voltage isapplied across electrodes 247, the shape of region 244 acts as a lensand focuses S-polarized display light at a focal length 262. In someembodiments, focus signal 254 is a voltage that is applied acrosselectrodes 247.

FIG. 2C illustrates tunable lens 253 that operates using a similarconcept as tunable lens 253. However, in FIG. 2C, tunable lens 253retains optical power for S-polarized display light even when it isunswitched due to the curve of the second electrode 257 also being theexiting side of tunable lens 253 that is not parallel to the receivingside of tunable lens 253. When tunable lens 253 is switched, theorientation of liquid crystals 259 changes which changes the refractiveindex encountered by S-polarized display light. The different refractiveindex changes the focal length (and corresponding optical power) of thetunable lens 253 by a focal length delta 272.

FIGS. 2D and 2E shows a tunable liquid lens 263 that can be used astunable lens 233, in accordance with an embodiment of the disclosure.FIG. 2D shows tunable liquid lens 263 when a voltage is applied toelectrodes 266. Utilizing hydrophobic principles, the voltage onelectrodes 266 generates electrostatic pressure 278 that bends theinterface between the illustrated water and oil in tunable liquid lens263. In FIG. 2D, electrostatic pressure 278 give tunable liquid lens 263positive (converging) optical power. In FIG. 2E, no voltage is appliedto electrodes 266, which relaxes the electrostatic pressure and tunableliquid lens 263 has negative (diverging) optical power.

Referring back to FIG. 2A, control circuitry 250 may be coupled tocontrol display module 205 to include different images in image light207. In one embodiment, control circuitry 250 is configured to controldisplay module 205 to include a first image, a second image, and a thirdimage in image light 207 while also controlling tunable lens 233 toadjust tunable lens 233 to a first focal length 241 while the firstimage is displayed, adjusting tunable lens 233 to a second focal length242 while the second image is displayed, and adjusting tunable lens 233to a third focal length 243 while the third image is displayed. Althoughfocal lengths 241, 242, and 243 are only illustrated from reflectiveelement 235 in FIG. 2A, focal lengths 241, 242, and 243 of tunable lens233 are measured along an optical path from tunable lens 233 to a givenfocal point. The effect of choosing different focal lengths (e.g. 241,242, and 243) allows optical system 200 to present three images withassociated depths in the same eyeward-region 276. The focal point(illustrated as black filled circles) from each focal length may bebehind eye 160 in order to produce virtual images that a viewer's eye160 can focus on. Those skilled in the art will appreciate that eventhough the focal points of the various focal lengths are illustratedbehind eye 160, the lens in eye 160 will further focus images in imagelight 207 onto the back of the eye so they will be in focus for theuser.

Control circuitry 250 may be configured to interlace images at afrequency (e.g. 240 Hz.) that is imperceptible to a human eye 160. Inone example, the first image is displayed for 10 ms while tunable lens233 is at the first focal length 241, no image is displayed for 1 mswhile tunable lens is adjusted to the second focal length 242, thesecond image is then displayed for 10 ms while tunable lens 233 is atthe second focal length 242, no image is displayed for 1 ms whiletunable lens 233 is adjusted to the third focal length 243, and thenthird image is then displayed for 10 ms while tunable lens 233 is at thethird focal length 243. The 1 ms periods of time where no image isdisplayed ensures that images are not displayed while tunable lens 233is transferring between focal lengths.

FIG. 2F illustrates computer generated images directed into differentdepths of the same eye-ward region 276 by tunable lens 233, inaccordance with an embodiment of the disclosure. In FIG. 2F, the firstimage is illustrated as the letter “A” and is presented to eye 160 at afirst focus depth 291. The second image is illustrated as the letter “B”at a second focus depth 292. The third image is illustrated as theletter “C” at a third focus depth 293. The first, second, and thirdimages are focused in the same x-y coordinates of eyeward-region 276,but they have different depths (z-axis). The virtual images (e.g. first,second, and third images) in image light 207 may be located in the rangeof a few meters in front of the viewer's eye 160, depending on whatfocal length of tunable lens 233 is presenting the image. In oneexample, the first image is presented at one meter, the second image ispresented at two meters, and the third image is presented at threemeters. A user may perceive a superimposed combination of the first,second, and third images, due to their different depths.

FIG. 3A illustrates control circuitry 350 controlling a stackedswitchable lens 340 that receives image light 207 to be directed intodifferent eyeward-regions, in accordance with an embodiment of thedisclosure. Display module 305 generates image light 207 that propagatesthrough stacked switchable lens 340 and combiner 330 includes areflective element 235 that directs image light 207 to eyeward regions375, 376, and 377. Display module 305 may be substantially similar todisplay module 205 and combiner 330 may be substantially similar tocombiner 230. Control circuitry 350 may include a processor, a FieldProgrammable Gate Array (“FPGA”), or other processing logic. Controlcircuitry 350 may include buffers and/or memory to store instructions,settings, images, and other data.

Stacked switchable lens 340 is a transmissive stacked switchable lens340, in the illustrated embodiment. FIG. 3B illustrates controlcircuitry 350 coupled to selectively activate a first switching optic341, a second switching optic 342, and a third switching optic 343. Eachswitching optic, when activated, has a static prescription. Theprescriptions for the different switching optics may vary by off-axisamount and/or focal length. When the switching optic is not activated,it has no prescription and is substantially transparent.

In FIG. 3B, when control circuitry 350 activates switching optic 341(and switching optics 342 and 343 are not activated and substantiallytransparent), image light 207 is directed in direction 361 because theprescription of switching optic 341 includes off-axis lensingproperties. When control circuitry 350 activates switching optic 342(and switching optics 341 and 343 are not activated and substantiallytransparent), image light 207 is directed in direction 362. In theillustrated embodiment, switching optic 342 may not necessarily includeoff-axis lensing properties. In other embodiments, switching optic 342includes off-axis properties. When control circuitry 350 activatesswitching optic 343 (and switching optics 341 and 342 are not activatedand substantially transparent), image light 207 is directed in direction363.

Control circuitry 350 is also coupled to display module 305, in FIG. 3B.Control circuitry 350 may be configured to control display module 305 toinclude a first image in image light 207 while activating switchingoptic 341 (and not activating switching optics 342 and 343) so that thefirst image is directed in direction 361. Then, control circuitry maydeactivate switching optic 341 and activate switching optic 342 whiledirecting display module 305 to include a second image in image light207 so that the second image will be directed in direction 362. Displaymodule 305 may then include a third image in image light 207 (at thedirection of control circuitry 350) while activating switching optic 343(while switching optics 341 and 342 are deactivated) so that the thirdimage is directed in direction 363. The images may be interlaced at afrequency high enough to be imperceptible to the human eye, due to thepersistence of the images on eye 160. In other words, display module 305may cycle through the displayed images fast enough to be unnoticed by auser (the user will perceive that the first, second, and third imagesare displayed simultaneously), due to the persistence of light on eye160

In FIG. 3B, control circuitry 350 may be connected to a network toreceive and transmit information. In the illustrated embodiment, controlcircuitry 350 is using a communication link 320 (e.g., a wired orwireless connection) to a remote device 325, which may be a server.Control circuitry 350 may receive data from remote device 325, andconfigure the data for display with display module 305. Remote device325 may be any type of computing device or transmitter including alaptop computer, a mobile telephone, or tablet computing device, etc.,that is configured to transmit data to control circuitry 350. Remotedevice 325 and control circuitry may contain hardware to enable thecommunication link 320, such as processors, transmitters, receivers,antennas, etc. Further, remote device 325 may take the form of or beimplemented in a computing system that is in communication with andconfigured to perform functions on behalf of a client device, such as anHMD.

In FIG. 3B, communication link 320 is illustrated as a wirelessconnection; however, wired connections may also be used. For example,the communication link 320 may be a wired serial bus such as a universalserial bus or a parallel bus. A wired connection may be a proprietaryconnection as well. The communication link 320 may also be a wirelessconnection using, e.g., Bluetooth® radio technology, communicationprotocols described in IEEE 802.11 (including any IEEE 802.11revisions), Cellular technology (such as GSM, CDMA, WiMAX, or LTE), orZigbee® technology, among other possibilities. The remote device 325 maybe accessible via the Internet and may include a computing clusterassociated with a particular web service (e.g., social-networking, photosharing, address book, etc.).

FIG. 3C illustrates an examples of a switching optic configuration thatcan be utilized within stacked switchable lens 340, in accordance withan embodiment of the disclosure. FIG. 3C shows a switchable holographicoptic technology that is known as holographic polymer dispersed liquidcrystal (“HPDLC”). While a HPDLC is activated (switched on), it affectslight according to the laws of the holographic optics recorded in theholographic medium. However, while the switchable hologram isdeactivated (switched off), the switchable holographic optic may appearessentially transparent to light that encounters the switchableholographic optic, and act as a simple transparent window. When theswitchable holographic optic is switched off, it may slightly affect thelight that encounters it because of an index of refraction changeassociated with the holographic medium. As a brief overview, HPDLCtechnology uses electrical stimulation to align liquid crystals (mixedwith a photoactive hologram medium) to form diffractive gratings. Theelectrical stimulation may then rotate the liquid crystals patterns toappear essentially transparent for a specific polarization, such thatthe liquid crystals are no longer forming diffractive gratings. HPDLCtechnology may be switchable from on to off in 50 us or faster, forexample. HDPLC technology is available for purchase from SGB Labs inSunnyvale, Calif.

In FIG. 3C, liquid crystals are disposed on both sides of an etchedsurface that is etched as a diffractive grating. When no voltage isapplied to ITO electrodes of HDPLC lens 344 (unswitched), the refractiveindex encountered by S-polarized light is the same and HDPLC lens 344 isessentially transparent to incident S-polarized light. However, when avoltage is applied to the ITO electrodes of HDPLC lens 344 (switched),the refractive index between the ITO electrodes changes and since one ofthe ITO electrodes is shaped as diffractive grating, the diffractivegrating at the interface between the two different refractive indexes“acts” on incoming S-polarized light. In the illustrated embodiment, thediffractive grating has positive optical power and focuses theS-polarized light at a focal length. The HDPLC lens 344 illustrated inFIG. 3C may be used as switching optic 342 when switching optic 342 doesnot include off-axis lensing properties. When a switching optic (e.g.341 and 343) includes off-axis lensing properties, the off-axis lensingproperties can be “written” into the hologram of the HDPLC lens.

In one embodiment, each switching optic (e.g. 341-343) is tuned to acton specific wavelengths of light (using Bragg selectivity principles)based on the angle that image light 207 from display module 305 willencounter the switching optic. Each switching optic may have only oneBragg selectivity to one specific spectrum (spectral bandwidth), or onespecific angle (angular bandwidth) and those holographic optics may bereferred to as having “singular selectivity.” Each switching optic mayalso be configured to include more than one Bragg selectivity, as it ispossible to “record” more than one Bragg selectivity into a givenholographic medium. Consequently, when activated, each of switchingoptics 341, 342, and 343 may be configured to direct multiple specificspectrums (e.g. red, green, and blue) of image light 207 toward eye 160.In one embodiment, each switching optic has three Bragg selectivewavelengths and a significant amount of image light 207 is centeredaround the three Bragg selective wavelengths. Switching opticsconfigured to operate on more than one specific spectrum (having morethan one Bragg selectivity) may be referred to as having “pluralselectivity.”

FIG. 3D illustrates computer generated images directed into differenteyeward-regions 375, 376, and 377 that are stitched together, inaccordance with an embodiment of the disclosure. Eyeward-regions 375,376, and 377 are within a user's FOV 390. First switching optic 341,when activated, directs image light 207 to first eyeward-region 375. InFIG. 3D, the first image in eyeward-region 375 is illustrated as anenvelope. Second switching optic 342, when activated, directs imagelight 207 to second eyeward-region 376. The second image ineyeward-region 376 is illustrated as a monthly calendar. Third switchingoptic 343, when activated, directs image light 207 to thirdeyeward-region 377. The third image in eyeward-region 377 is illustratedas the word “SOCIAL.”

In FIG. 3D, the first, second, and third images are stitched together asa contiguous image having a 45° FOV, which increases the 15° FOVillustrated in FIG. 1B. Furthermore, the FOV is increased withoutnecessarily requiring an increase in the size of display module 305 orshortening the focal length of the optical combiner, which is prone tocreate a “bug eye” aesthetic because of the curvature requirements ofthe combiner lens. Instead, the amount of off-axis in each of the first,second (if any), and third switching optics 341, 342, and 343 isdesigned to create the contiguous image with a 45° FOV. It is understoodthat a user's eye 160 may look straight ahead to view the second imagein eyeward-region 376, slightly to the left to view eyeward-region 375,and slightly to the right to view eyeward-region 377, in someembodiments. In the illustrated embodiment, the first, second, and thirdimages are all at approximately the same depth (z-axis) because theircorresponding switching optics have the same focal length. However, itis appreciated that adjusting the focal length of the first, second, andthird switching optics 341, 342, and 343 will have corresponding changesin the depth of the images in FOV 390. In one embodiment, off-axislensing properties are written into switching optics 341 and 343, butswitching optic 342 includes no off-axis lensing properties.

FIG. 3E illustrates computer generated images directed into differenteyeward-regions 375, 376, and 377 that are not stitched together, inaccordance with an embodiment of the disclosure. Similarly to FIG. 3D,eyeward-regions 375, 376, and 377 are within a user's FOV 390. However,in FIG. 3E the first, second, and third images are not stitched togetheras a contiguous image. However, the user's FOV is still extended fartherthan the 15° FOV illustrated in FIG. 1B. The amount of off-axis in eachof the first, second, and third switching optics is designed to createthe noncontiguous images, in FIG. 3E. It is appreciated that adjustingthe off-axis amount of the different switching optics can move thefirst, second, and third images within the users FOV 390, as desired. Inthe illustrated embodiment, the first, second, and third images are allat the same depth (z-axis) because their corresponding switching opticshave the approximately the same focal length. However, it is appreciatedthat adjusting the focal length of the first, second, and thirdswitching optics is possible and will have corresponding changes in thefocus depth of images in FOV 390.

In both embodiments illustrated in FIGS. 3D and 3E, control circuitry350 may cause display module 305 to interlace the first, second, andthird images into image light 207. Control circuitry 350 may thenactivate first switching optic 341 (to direct the first image toeyeward-region 375) when the first image is included in image light 207,activate second switching optic 342 (to direct the second image toeyeward region 376) when the second image is included in image light207, and activate third switching optic 343 (to direct the third imageto eyeward-region 377) when the third image is included in image light207. Control circuitry 350 may orchestrate the interlacing of the imagesat a refresh rate (e.g. 240 Hz) that generates persistent images uponeye 160.

FIG. 4A illustrates a display module 405 launching image light 207 andcontrol circuitry 450 coupled to control a reconfigurable lens 433positioned to direct image light 207 into different eyeward-regions 375,376, and 377, in accordance with an embodiment of the disclosure.Display module 405 generates image light 207 and reconfigurable lens 433receives image light 207 and directs image light 207 to eyeward-regions375, 376, and 377, depending on a lens state of reconfigurable lens 433.Display module 405 may be substantially similar to display module 205and combiner 430 may be substantially similar to combiner 230. Controlcircuitry 450 may include a processor, a Field Programmable Gate Array(“FPGA”), or other processing logic. Control circuitry 450 may includebuffers and/or memory to store instructions, settings, images, and otherdata.

In FIG. 4A, control circuitry 450 is coupled to a reconfigurable lens433 and reconfigurable lens 433 is reconfigurable into different lensstates in response to lens configuration signal 451. Lens configurationsignal 451 may be digital or analog. The optical power and off-axisproperties of each lens state of reconfigurable lens 433 may beconfigured within the constraints of reconfigurable lens 433.Reconfigurable lens 433 can be tuned to different lens statesarbitrarily (within its constraints) in real time. Control circuitry 450may cause display module 405 to interlace a first, second, and thirdimage into image light 207. Control circuitry 450 may then reconfigurelens 433 to a first lens state to direct the first image toeyeward-region 375 when the first image is included in image light 207,reconfigure lens 433 to a second lens state to direct the second imageto eyeward-region 376 when the second image is included in image light207, and reconfigure lens 433 to a third lens state to direct the thirdimage to eyeward-region 377 when the third image is included in imagelight 207. Control circuitry 450 may orchestrate the interlacing of theimages at a refresh rate (e.g. 120 Hz) that generates persistent imagesupon eye 160. Reconfiguring the reconfigurable lens 433 to differentlens states (each with their own optical power and off-axis properties)in concert with generating images with display module 405 can achievethe arrangement of the first, second, and third images as one contiguouspersistent image, as illustrated in FIG. 3D. Similarly, optical system400 can achieve the arrangement of the first, second, and third images,as illustrated in FIG. 3E.

FIGS. 4B-D illustrates example reconfigurable optic configurations thatcan be utilized in reconfigurable lens 433 in FIG. 4A, in accordancewith an embodiment of the disclosure. More specifically, FIGS. 4B-Dillustrates reconfigurable reflective lenses that can be integrated intodeformable lenses or micro-electro-mechanical systems. FIG. 4B shows avarious efficiency grating, FIG. 4C shows a blazed grating, and FIG. 4Dshows a diffractive lens. In FIGS. 4B and 4C, A represents the gratingperiod produced by the dynamic element(s) of the reconfigurablereflective lens and δ represents the size of a single element of thereconfigurable reflective lens. Switchable diffractive lenses can besourced from Holo-eye of Germany and from Light Blue Optics of theUnited Kingdom. In these reconfigurable lenses, the off-axis and thefocal length can be tuned arbitrarily (via lens configuration signal451) in real time.

FIG. 5 depicts a top view of a user wearing a binocular head mounteddisplay that includes a dynamic lens, in accordance with an embodimentof the disclosure. Each optical combiner 530 may be implemented with anembodiment of optical combiners 230, 330, or 430. Element 532 may be areflective element 235 or reconfigurable lens 433, depending on theembodiment that is utilized. Although not illustrated, tunable lens 233or stacked switchable lens 340 may be disposed between element 532(which would be reflective element 235) to achieve the embodiments ofFIGS. 2A and 3A, respectively. Display module 505 may be implementedwith display modules 205/305/405.

Optical combiners 530 are mounted to a frame assembly, which includes anose bridge 506, left ear arm 510, and right ear arm 515. Although FIG.5 illustrates a binocular embodiment, HMD 500 may also be implemented asa monocular HMD. The two optical combiners 530 are secured into an eyeglass arrangement that can be worn on the head of a user. The left andright ear arms 510 and 515 rest over the user's ears while nose bridge506 rests over the user's nose. The frame assembly is shaped and sizedto position each optical combiner 530 in front of a corresponding eye160 of the user. Of course, other frame assemblies having other shapesmay be used (e.g., a visor with ear arms and a nose bridge support, asingle contiguous headset member, a headband, goggles type eyewear,etc.).

The illustrated embodiment of HMD 500 is capable of displaying anaugmented reality to the user. Each optical combiner 530 permits theuser to see a real world image via external scene light 155. Left andright (binocular embodiment) image light 207 may be generated by displaymodules 505 mounted to left and right ear arms 510 and 515. Image light207 (after being reflected by element 532) is seen by the user as avirtual image superimposed over the real world as an augmented reality.

The processes explained above are described in terms of computersoftware and hardware. The techniques described may constitutemachine-executable instructions embodied within a tangible ornon-transitory machine (e.g., computer) readable storage medium, thatwhen executed by a machine will cause the machine to perform theoperations described. Additionally, the processes may be embodied withinhardware, such as an application specific integrated circuit (“ASIC”) orotherwise.

A tangible non-transitory machine-readable storage medium includes anymechanism that provides (i.e., stores) information in a form accessibleby a machine (e.g., a computer, network device, personal digitalassistant, manufacturing tool, any device with a set of one or moreprocessors, etc.). For example, a machine-readable storage mediumincludes recordable/non-recordable media (e.g., read only memory (ROM),random access memory (RAM), magnetic disk storage media, optical storagemedia, flash memory devices, etc.).

The above description of illustrated embodiments of the invention,including what is described in the Abstract, is not intended to beexhaustive or to limit the invention to the precise forms disclosed.While specific embodiments of, and examples for, the invention aredescribed herein for illustrative purposes, various modifications arepossible within the scope of the invention, as those skilled in therelevant art will recognize.

These modifications can be made to the invention in light of the abovedetailed description. The terms used in the following claims should notbe construed to limit the invention to the specific embodimentsdisclosed in the specification. Rather, the scope of the invention is tobe determined entirely by the following claims, which are to beconstrued in accordance with established doctrines of claiminterpretation.

What is claimed is:
 1. A Head Mounted Display (“HMD”) comprising: adisplay module to generate image light; an optical combiner forcombining the image light with external scene light, wherein the opticalcombiner includes a reflective element coupled to receive the imagelight and direct the image light in an eye-ward direction; a tunablelens positioned to receive the image light and configured to adjust afocal length of the tunable lens to focus the image light at varyingfocus depths; and control circuitry configured to output a focus signalto control adjusting the focal length of the tunable lens.
 2. The HMD ofclaim 1, wherein the control circuitry is configured to control thedisplay module to include at least a first image and a second image inthe image light, and wherein the control circuitry is configured toselect a first focal length of the tunable lens when the first image isincluded in the image light and configured to select a second focallength of the tunable lens when the second image is included in theimage light, the first focal length different from the second focallength.
 3. The HMD of claim 2, wherein the first image and the secondimage are interlaced in the image light at a frequency high enough to beimperceptible to a human eye.
 4. The HMD of claim 2, wherein the controlcircuitry is configured to control the display module to include a thirdimage in the image light, and wherein the control circuitry isconfigured to select a third focal length of the tunable lens when thethird image is included in the image light, the third focal lengthdifferent from the first and second focal lengths.
 5. The HMD of claim2, wherein the first image and the second image are presented atdifferent focus depths within the same eyeward region.
 6. The HMD ofclaim 1, wherein the tunable lens is disposed between the display moduleand the reflective element.
 7. The HMD of claim 1, wherein the tunablelens includes liquid crystals disposed between two electrodes and theliquid crystals are configured to change orientation in response to thefocus signal received from the control circuitry, and wherein changingthe orientation of the liquid crystals adjust the focal length of thetunable lens.
 8. The HMD of claim 1, wherein the tunable lens includes atunable liquid lens that changes electrostatic pressure in liquid toresponse to the focus signal received from the control circuitry,wherein changing the electrostatic pressure adjusts the focal length ofthe tunable lens.
 9. A Head Mounted Display (“HMD”) comprising: adisplay module to generate image light; an optical combiner forcombining the image light with external scene light, wherein the opticalcombiner includes a reflective element coupled to receive the imagelight and direct the image light in an eye-ward direction; a stackedswitchable lens optically coupled to receive the image light, whereinthe stacked switchable lens includes at least a first switching opticand a second switching optic; and control circuitry configured toselectively activate the first switching optic and the second switchingoptic, wherein the first switching optic is configured to direct theimage light toward a first eyeward region when activated by the controlcircuitry, and wherein the second switching optic is configured todirect the image light toward a second eyeward region when activated bythe control circuitry, the first eyeward region different from thesecond eyeward region.
 10. The HMD of claim 9, wherein the controlcircuitry is configured to control the display module to include atleast a first image and a second image in the image light, and whereinthe control circuitry is configured to activate the first switchingoptic when the first image is included in the image light and configuredto activate the second switching optic when the second image is includedin the image light.
 11. The HMD of claim 10, wherein the first image andthe second image are interlaced in the image light at a frequency highenough to be imperceptible to a human eye.
 12. The HMD of claim 10,wherein the stacked switchable lens includes a third switching opticconfigured to direct the image light toward a third eyeward region whenactivated by the control circuitry, and wherein the control circuitry isconfigured to control the display module to include a third image in theimage light when activating the third switching optic, the third eyewardregion different from the first and second eyeward regions.
 13. The HMDof claim 10, wherein the first switching optic has a shorter focallength than the second switching optic, and wherein the first image ispresented at a shorter focus depth than the second image.
 14. The HMD ofclaim 9, wherein the first switching optic has a same focal length asthe second switching optic.
 15. The HMD of claim 9, wherein the stackedswitchable lens is disposed between the display module and thereflective element to direct the image light to a given eyeward regionvia the reflective element.
 16. The HMD of claim 9, wherein the firstswitching optic includes a first holographic polymer-dispersed liquidcrystals (“H-PDLC”), and the second switching optic includes a secondH-PDLC.
 17. The HMD of claim 9, wherein the first switching optic givesoff-axis lensing to the image light when activated, and wherein thefirst switching optic is substantially transparent and givessubstantially zero lensing to the image light when unactivated.
 18. AHead Mounted Display (“HMD”) comprising: a display module to generateimage light; control circuitry coupled to control the display module toinclude at least a first image and a second image in the image light;and a reconfigurable lens optically coupled to receive the image lightand dynamically reconfigure in response to a lens configuration signalgenerated by the control circuitry, wherein the control circuitry isconfigured to select a first lens state of the reconfigurable lens todirect the first image to a first eyeward region when the first image isincluded in the image light and configured to select a second lens stateof the reconfigurable lens to direct the second image to a secondeyeward region when the second image is included in the image light, andwherein the first image and the second image are interlaced in the imagelight at a frequency high enough to be imperceptible to a human eye. 19.The HMD of claim 18, wherein the control circuitry is configured tocontrol the display module to interlace a third image in the imagelight, and wherein the control circuitry is configured to select a thirdlens state of the reconfigurable lens when the third image is includedin the image light, the third lens state directing the third image to athird eyeward region different from the first and second eyewardregions.
 20. The HMD of claim 18, wherein the first lens state has ashorter focal length than the second lens state, and wherein the firstimage is presented at a shorter focus depth than the second image. 21.The HMD of claim 18, wherein the first lens state has a same focallength as the second lens state.
 22. The HMD of claim 18, wherein thesecond lens state includes off-axis properties.